Project Summary/Abstract Recent developments in the field of immunotherapy clearly support the contribution of the immune system in eradicating cancer. Histone deacetylase (HDAC) inhibitors are currently employed in the treatment of many malignancies, and accumulating evidence suggests that many of the anticancer effects of HDAC inhibitors involve the immune system. Previously, there was limited information on the role of HDAC11 in immunity and cancer. We discovered that HDAC11 negatively regulates IL-10 production in antigen-presenting cells. We also found that HDAC11 is highly expressed in T lymphocytes and neutrophils and, subsequently, revealed that HDAC11 disruption in T cells is associated with an enhanced pro-inflammatory cytokine profile and effector molecule production. T cells lacking HDAC11 are less susceptible to regulatory T cell suppression in vitro, are refractory to tolerance induction in vivo, and display enhanced anti-tumor responses in transplanted mantle cell lymphoma murine models. Furthermore, HDAC11 is a multifaceted regulator of neutrophils. The absence of Hdac11 in neutrophils significantly increases cellular production of proinflammatory cytokines and promotes cell migration and phagocytic capacity. More recently, our group discovered an efficient novel activity for HDAC11, the removal of long-chain fatty acyl groups from protein lysine residues. This novel activity is >10,000-fold more efficient than its deacetylase activity. Using a syngeneic mouse-to-mouse model, we established ectopic tumors in Hdac11 wildtype and knockout (KO) mice. The growth of the syngeneic lymphoma cells in the Hdac11 KO mice was markedly inhibited, pointing toward a crucial role of HDAC11 in the tumor microenvironment. In this resubmission application, the central hypothesis is that HDAC11 reprograms anti-cancer immunity via its defatty-acylation activity and presents a potential novel drug target for cancer treatment. Our long-term goal is to develop a detailed molecular understanding of HDAC11's role in anti-tumor immunity. Results from this work will: (1) provide a better understanding of the anti-tumor behavior of HDAC11; (2) expand a functional understanding of protein lysine defatty-acylation in cancer; (3) develop better treatment strategies for cancer through targeting the lysine defatty-acylation mechanism; and (4) produce selective HDAC11 inhibitors, which will accelerate the development of new cancer treatment strategies.